Right, I get that playing a minion is better than playing nothing at all, and definitely agree that the ghoul and ghast can be pretty useful. However, I have rarely encountered a circumstance in which I was unable to summon a creature that was worth points. However, this could be because I've only played two-player games. It might be harder to summon even lesser servitors in a 3 or 4 player game. The trade minions might also be more useful in such circumstances - more to choose from.

Yeah, I've used Dhole for the same thing - quite helpful in the right circumstance.